Validation of the periodicity of growth zone deposition in otoliths of two large endemic Labeobarbus species in Lake Tana, Ethiopia

Although validation of the rate of growth zone deposition is a prerequisite for accurate age estimation, such studies are non-existent for the endemic Labeobarbus species in Lake Tana. Therefore, the aim of the current study was to validate the periodicity of growth zone deposition in asteriscus otolith of L. tsanensis and L. platydorsus. A total of 723 and 496 asteriscus otolith pairs from L. tsanensis and L. platydorsus, respectively, were examined. Binary- circular models, based on edge analysis (EA) and linear-circular models, based on marginal increment analysis (MIA) were employed to validate the rate of growth zone deposition. The results of EA indicate that there is an annual growth zone deposition for L. tsanensis and L. platydorsus. For both species, the highest proportion of translucent zones was detected between October and January, with a peak in January. The results of the MIA corroborated this for both species. In addition, the lowest marginal increment ratio (MIR) was recorded in January for both species. The annual growth zone deposition in asteristicus otoliths of these species is likely caused by the relatively low water temperature coinciding with the peak breeding activity of the species.